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x in (-oo:+oo)
(2/15)*x^2 = 27/10 // - 27/10
(2/15)*x^2-(27/10) = 0
(2/15)*x^2-27/10 = 0
2/15*x^2 = 27/10 // : 2/15
x^2 = 81/4
x^2 = 81/4 // ^ 1/2
abs(x) = 9/2
x = 9/2 or x = -9/2
x in { 9/2, -9/2 }
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